Spinning bath



Patented July 28, 1942 SPINNING BATH Kenneth E. Smith, Elizabethton, Tenn., assignor to North American Rayon Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application October 7, 1938, Serial No. 233,804

4 Claims.

My present invention relates to manufacture of filaments of artificial origin by the viscose spinning process, but more specifically it refers to the preparation of the spinning bath used for the precipitation of the spun filaments.

In the manufacture of artificial silk by the viscose spimiing process, wood pulp or some other form of cellulose is treated with lye, shredded etc., treated with carbon disulphide to form a cellulose xanthate, made up into a solution containing from 6-8% of cellulose and then spun or extruded through minute orifices into a liquid capable of regenerating the solution, 1. e., forming from the solution threads of cellulose. The bath or liquid into which the filaments thus formed are expressed or extruded is called a setting bath or coagulating bath. My present invention has to do broadly with such a bath.

One object of the present invention is to provide a bathimwhich the percentage of soluble lead is maintained and controlled.

Another object of my invention is to so control the percentage of lead in the bath that discoloration of the yarn is prevented.

Another object of my present invention is to provide a novel manner for controlling the lead content of viscose baths at a low cost so that subsequent spoiling of spooled yarn, due to excess I of lead, is eliminated.

These and other objects of my present invention will be clearly discernible from a consideration of the following specification and the appended claims.

In the viscose process used commercially it is necessary to maintain a supply of sulphuric acid and to make up a so-called setting or coagulating bath solution containing this sulphuric acid. Such a bath solution would contain in addition to approximately 10-12% sulphuric acid, other salts such as sodium sulphate (approximately 2-25%), magnesium sulphate (approximately 5-6%), possibly other chemicals, andwater to make-up the 100%. This bath, in the commercial plant, is prepared and continually circulated through a system whereby it is:

1. Prepared and circulated in lead tanks,

2. Pumped through filters,

3. Pumped through the spinning bath containers.

4. Rejuvenated through the addition of sufficient chemicals to maintain its strength and,

5. Returned to the original container for reuse.

The presence of lead from the containers employed is noticeable in both soluble and insoluble form in this solution. If the lead content, of the spinning bath exceeds a certain concentration, the portions of the spinning bath adhering to the yarn and the sulphides present in the atmosphere tend to discolor the yarn thus formed. When excess of lead is in the system due to a slightly longer standing in the pipes and tanks, or a slowing down of the customary production, or any other reason, this lead finds its way into the yarn and chemicals in the air, more especially sulphur from small traces of hydrogen sulphide combine to form a discoloration of the yarn. Subsequent washing operations as usually employed act to remove a great amount of these lead impurities but sufiicient amounts of lead impurities are present to spoil a great many spools of yarn. As an example of the amount of spoilage which may omur it might be mentioned that for an output of, for example, aproximately 2,000,000 pounds of yarn it is possible that three or four thousand pounds of yarn might be spoiled. The loss entailed, for example, 4,000 pounds of yarn produced over a period of several weeks, would amount of around $2,000. When one compares this with the cost of my present invention (approximately 8 to 10 cents per day for the chemicals employed for the same period of time) it is readily seen that my new invention has a financial as well as a technical importance.

My new invention consists essentially in the use of sodium trithiocarbonate in small amounts in the spinning bath solution to be used. Because of the very small amounts which are necessary in order to produce the desired result, only a small cost (6 to 8 cents a day) to prepare sodium trithiocarbonate will be involved. This sodium trithiocarbonate may be fed to the spinning solution system in small amounts throughout the day in order to maintain a suflicient concentration to secure the desired results. For example, if a daily output of a single plant is thirty or forty thousand pounds only three or four hundred grams of sodium trithiocarbonate would be necessary over a .period of time involving several weeks or months.

0th" r trithiocarbonates, for instance potassium trlthif arbonate, might be employed to produce the same result. The relatively cheap sodium trithiocarbonate is considered the most practical foruse in a setting bath containing sodium ions.

In carrying out my new invention it has been found, as pointed out above, that only a few hundred grams of sodium trithiocarbonate would be necessary to prevent an excess of soluble lead in several million pounds of yarn. In a typical spinning bath containing sulphuric acid, magnesium sulphate and sodium sulphate in the general proportions outlined above, I have found that ordinarily there are present in the spinnin bath both soluble and insoluble lead compounds and that the insoluble lead compounds are ordinarily removed by filtration in the normal procedure of production. By adding controlled amounts of sodium trithiocarbonate to the spinning bath prior to the filtration step these soluble lead compounds are reduced so that an excess of lead in the bath will-not be present. This is accomplished by the fact that lead reacts with the trithiocarbonate to produce an insoluble lead salt which is in return removed by filtration before the bath is used for the production of yarn. A suflicient amount of sodium trithiocarbonate is employed to reduce the lead content of the bath and maintain it at a concentration below 0.6 part per million. One specific example may be set forth by considering a case in which a spinning bath of 500 cubic meters is employed in the system. If it is found by analysis that the amount of soluble lead is, for example, two parts per million, only 372 grams of sodium trithiocarbonate need be added over a period of 36, 48 or more hours in order to maintain the amount of soluble lead in the bath at a percentage not exceeding 0.6 part per million. This low soluble lead content will be found to be insufiicient to produce the deleterious results enumerated above and no discoloration of the yarn due to the presence of an excess of soluble lead therein will be experienced. A normal bath containing less than 0.6 part per million of soluble lead will not, as pointed out above, cause bad effects to be produced. Smaller amounts of lead,-

1. e., amounts less than 0.6 part per million need not be removed from the bath and serve a useful purpose therein.

Having now set forth my invention as required by the patent statutes what I desire to claim is:

1. A method for controlling the proportion of soluble lead in spinning baths for use in the manufacture of yarn from viscose, which comprises treating the liquid which forms the spinning bath with controlled amounts of sodium trithiocarbonate capable of forming an insoluble lead compound and removing this compound from the bath.

2. A method for controlling the proportion of soluble lead in spinning baths for use in the manufacture of yarn from viscose, which comprises treating the liquid which forms the spinning bath with controlled amounts of sodium trithiocarbonate capable of reducing the soluble lead to less than .6 part per million, and then removing the precipitat thus formed from the bath.

3. A method for controlling the proportion of soluble lead in spinning baths for use in the manufacture of yarn from viscose, which comprises, treating the liquid which forms the spinning bath with controlled amounts of an alkali metal trithiocarbonate capable of forming an insoluble lead compound and removing this compound from the bath. I

4. A method for controlling the proportion of soluble lead in spinning baths for use in the,

manufacture of yam from viscose, which comprises treating the liquid which forms the spinning bath with controlled amounts of alkali metal trithiocarbonate-capable of reducing the soluble lead to less than-.6 part per million, and

then removing the precipitate thus formed fromthe bath.

KENNETH E. SMITH. 

